Photochemical Machining Process Defined

Photo Chemical Etching is also called Photo Chemical Milling, Photo Etching, Photofabrication and Chemical Etching.

This process is used in the production of precision parts and decorative items, mainly sheets and foils. In photo chemical etch, the unit of labor is the sheet.

Using photo etching, Newcut  can turn your CAD file, blueprint, or drawings into thin metal parts. The material specified is coated with a light sensitive polymer, imaged with a photo tool using UV light, developed much like film, and then chemically etched.

The results are precision components manufactured in most metals, including some exotics. Stainless Steel, aluminum, copper, and brass are the most popular metals used in this process.

Why Should You Use

Photo Chemical Etching

Designers, manufacturing engineers, and purchasing groups are recognizing the advantages photo chemical etching has to offer.

Some of the benefits of this unique manufacturing process are the ability to make a complex part that is beyond hard tool capability and to fabricate the part in dead soft or full hard material without burrs or metal distortion.

Another significant benefit is response time. An order may be filled in days, which allows the design to be proven without incurring the cost of a hard tool.

Photo etching is a growing industry, gaining experience and recognition as a viable method of working metal.

Step 1: Engineering

Accuracy is the byword of the photochemical etching technique, which produces thin gauge metal parts utilizing photo tools, light sensitive coatings and etching reagents…eliminating the burrs left by standard machining methods.

A unique feature of the Newcut photo etching technology is that it provides parts that are free of any tabbing during the processing.

Step 2: Incoming

Newcut can photo etch a wide range of metals and alloys including Molybdenum, Hastelloy X, Nickel Silver, Silicon Steel, and Titanium, as well as the more common metals in any quantities.

If you don't see the material for your photochemical machining project on our Materials List, please contact us.

Step 3: Cutting

The bulk metal sheets are cut to an optimum size to reduce waste and allow for efficient use of the coating material used in later steps of the photochemical machining process.

Newcut engineers will specify the largest sheet size possible consistent with the size and dimensional tolerances of your part.

Step 4: Cleaning

Metal cleaning or prep is next in our process; the importance of this step cannot be overemphasized.

Proper metal preparation, degreasing, and the removal of surface contaminants is essential for proper adhesion between the raw material and the photo resist during the coating process.

Why Is Cleaning So Critical To The Photo Etching Process?

Most photo resists have been developed for the printed circuit industry and have adequate adhesion to copper and copper alloys.

Care must be taken to promote adhesion when other materials are etched, especially stainless steel.

What Is Passivation

Passivation or pre-etchings are considerations as well as abrasion by mechanical means to texture the surface to be coated.

Modern PCM companies have invested in “clean lines” for improved material cleanliness.  These conveyorized machines are typically multi-chambered and material is put through a series of clean and rinses to ensure proper surface condition. 

The quality and quantity of the finished parts depends greatly on the care taken during this step.

Step 5: Coating

In any Photochemical Machining process, the material should be coated with photo resist directly after cleaning.  This reduces the chance of surface contamination and oxidation.

The coating is photosensitive and resistant to the etchant used to cut the chosen metal.  Dry film or liquid resist is applied to both sides of the work piece to allow etching for both sides simultaneously.

Using Photo Resists In The Photochemical Etching Process

Photo resist can be either a positive or negative masking. 

In positive masking the areas exposed to light during the imaging process wash away during the development stage. 

In the more commonly used negative masking the areas exposed to the UV light are bonded to the material and the non exposed areas are rinsed away during the development process.

Advances in resist technology combined with new and improved Computer Assisted Design (CAD) artwork have enabled photochemical etching companies to expose, develop and etch features not thought possible a few years ago.

Step 6: Exposing

During this step in the photo etching process, material with the photosensitive coating is exposed to UV light. This is a straightforward process that transfers the photo tool image onto the coated material.

Types Of Imaging Used
In Photochemical Etching

Imaging has been accomplished by exposing the coated material to sunlight; however in the northeast it is more practical to utilize more sophisticated equipment that will control the desired exposure length and intensity.

Types Of Equipment Used In
Photochemical Etching

Exposure equipment commonly used in the Photo Chemical Etching industry consists of a vacuum frame, high intensity UV light and multiple trays for more economical transfer of image.

The coated material is sandwiched between the registered film tooling and exposed from both sides; this exposure polymerized the areas of the film tool.

Step 7: Developing

After exposing, the sheets of material must be developed.

While development of materials can be performed in trays filled with developer, most Photo Chemical Etching companies use conveyor equipment.

During the run through the developer a liquid developer is sprayed onto the sheets and this removes the un-polymerized areas of the image.

Results Of Developing
In the PCM Process

What is left after developing is the metal sheet with the image of the design protected by photo resist. The unprotected areas of the sheet are ready to be removed by photochemical etching.

Step 8: Photo Etching

During the photochemical etching process any material not protected by the resist is eroded.  This means that as the chemicals cut through the metal they are also cutting laterally under the protective coating of photo resist.

When Does Breakout
Occur During Photo Etching?

When the process has etched halfway from both sides they reach a breakpoint. 

When breakout occurs the etchant can run through the holes and smooth the sidewalls.

What is Etch Factor

During the engineering of the film tool, compensation is required to produce parts within specific tolerances, this is called etch factor.

Step 9: Stripping

The next step in the manufacture of Photochemical Machined parts is stripping off the protective coating of photo resist.

Many companies use machines that have a strip chamber on the etch machines.  This is practical when running a product line, less practical when producing the varied parts most Photo Etching companies offer.

What Is The Most Used Method
Of Stripping Used IN PCM?

The most common method of parts stripping is to soften and lift the resist coating using the “batch” method.

Other PCM
Stripping Methods

Other processes dissolve the protective coating completely.  In either process care must be taken to ensure no resist material is left on the parts and staining or surface corrosion does not occur. 

Step 10: Quality Control

Before shipping, the finished parts are inspected.  These are the final steps in the photo etch process.

What Equipment Is Used In

Inspecting Photochemical Machined Parts?

From sampling to 100% inspection, a wide variety of inspection equipment is utilized. 

Plug and pin gauges are common inspection tools; more sophisticated optical comparators with the ability to program inspection requirements are also used.

Step 11: Forming

Depending on your application, the parts may need to be formed after the photo etching process has been completed. 

Our forming department consists of highly qualified personnel who take pride in their work and do an excellent job of “forming” your pieces to meet your rigid specifications.

Step 12: Final Product

Now that you're familiar with the photochemical etching process we hope you'll consider using Newcut for your next project. If you need it, we can more than likely make it!

Please give us a call or email us for more information.

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